Flattening portal bridge

ABSTRACT

A flattening portal bridge (FPB) is provided to support addressing according to a first addressing scheme and a second, alternative addressing scheme. The FPB comprises a primary side and a secondary side, the primary side connects to a first set of devices addressed according to a first addressing scheme, and the secondary side connects to a second set of devices addressed according to a second addressing scheme. The first addressing scheme uses a unique bus number within a Bus/Device/Function (BDF) address space for each device in the first set of devices, and the second bus addressing scheme uses a unique bus-device number for each device in the second set of devices.

This application is a divisional of and claims benefit from U.S. patentapplication Ser. No. 15/281,381, filed Sep. 30, 2016, which claimsbenefit to U.S. Provisional Patent Application Ser. No. 62/303,487,filed Mar. 4, 2016, all of which are hereby incorporated herein in theirentirety.

FIELD

This disclosure pertains to computing system, and in particular (but notexclusively) to address space mapping.

BACKGROUND

Peripheral Component Interconnect (PCI) configuration space is utilizedby systems employing PCI, PCI-X, and PCI Express (PCIe) to performconfiguration tasks of PCI-based devices. PCI-based devices have anaddress space for device configuration registers referred to asconfiguration space and PCI Express introduces extended configurationspace for devices. Configuration space registers are typically mapped tomemory mapped input/output locations by the host processor. Devicedrivers, operating systems, and diagnostic software access theconfiguration space and can read and write information to configurationspace registers.

One of the improvements the PCI Local Bus had over other I/Oarchitectures was its configuration mechanism. In addition to the normalmemory-mapped and I/O port spaces, each device function on the bus has aconfiguration space, which is 256 bytes long, addressable by knowing theeight-bit PCI bus, five-bit device, and three-bit function numbers forthe device (commonly referred to as the BDF or B/D/F, as abbreviatedfrom bus/device/function). This allows up to 256 buses, each with up to32 devices, each supporting eight functions. A single PCI expansion cardcan respond as a device and can implement at least function number zero.The first 64 bytes of configuration space are standardized; theremainder are available specification defined extensions and/or forvendor-defined purposes.

In order to allow more parts of configuration space to be standardizedwithout conflicting with existing uses, there can be a list ofcapabilities defined within the upper 192 bytes of Peripheral ComponentInterface configuration space. Each capability has one byte thatdescribes which capability it is, and one byte to point to the nextcapability. The number of additional bytes depends on the capability ID.If capabilities are being used, a bit in the Status register is set, anda pointer to the first in a linked list of capabilities is provided.Versions of PCIe have been provided with similar features, including anextended configuration space expanding the total size of configurationspace to 4096 bytes, and such as a PCIe extended capabilities structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a computing system including aninterconnect architecture.

FIG. 2 illustrates an embodiment of a interconnect architectureincluding a layered stack.

FIG. 3 illustrates an embodiment of a request or packet to be generatedor received within an interconnect architecture.

FIG. 4 illustrates an embodiment of a transmitter and receiver pair foran interconnect architecture.

FIG. 5 illustrates a representation of system buses.

FIG. 6 illustrates a representation of enumeration of bus identifiers ina system.

FIG. 7A illustrates a representation of system employing instances of aflattening portal bridge (FPB).

FIG. 7B illustrates an example implementation of a FPB.

FIG. 8 illustrates a detailed representation of an example FPB.

FIG. 9 illustrates example addresses in BDF space and supportedgranularities.

FIG. 10 illustrates the layout of addresses in the memory address spacebelow 4 GB to which the FPB MEM Low mechanism applies and the effect ofgranularity on these addresses.

FIG. 11 illustrates an embodiment of a block diagram for a computingsystem including a multicore processor.

FIG. 12 illustrates another embodiment of a block diagram for acomputing system.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth,such as examples of specific types of processors and systemconfigurations, specific hardware structures, specific architectural andmicro architectural details, specific register configurations, specificinstruction types, specific system components, specificmeasurements/heights, specific processor pipeline stages and operationetc. in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art thatthese specific details need not be employed to practice the presentinvention. In other instances, well known components or methods, such asspecific and alternative processor architectures, specific logiccircuits/code for described algorithms, specific firmware code, specificinterconnect operation, specific logic configurations, specificmanufacturing techniques and materials, specific compilerimplementations, specific expression of algorithms in code, specificpower down and gating techniques/logic and other specific operationaldetails of computer system haven't been described in detail in order toavoid unnecessarily obscuring the present invention.

Although the following embodiments may be described with reference toenergy conservation and energy efficiency in specific integratedcircuits, such as in computing platforms or microprocessors, otherembodiments are applicable to other types of integrated circuits andlogic devices. Similar techniques and teachings of embodiments describedherein may be applied to other types of circuits or semiconductordevices that may also benefit from better energy efficiency and energyconservation. For example, the disclosed embodiments are not limited todesktop computer systems or Ultrabooks™. And may be also used in otherdevices, such as handheld devices, tablets, other thin notebooks,systems on a chip (SOC) devices, and embedded applications. Someexamples of handheld devices include cellular phones, Internet protocoldevices, digital cameras, personal digital assistants (PDAs), andhandheld PCs. Embedded applications typically include a microcontroller,a digital signal processor (DSP), a system on a chip, network computers(NetPC), set-top boxes, network hubs, wide area network (WAN) switches,or any other system that can perform the functions and operations taughtbelow. Moreover, the apparatus', methods, and systems described hereinare not limited to physical computing devices, but may also relate tosoftware optimizations for energy conservation and efficiency.

As computing systems are advancing, the components therein are becomingmore complex. As a result, the interconnect architecture to couple andcommunicate between the components is also increasing in complexity toensure bandwidth requirements are met for optimal component operation.Furthermore, different market segments demand different aspects ofinterconnect architectures to suit the market's needs. For example,servers require higher performance, while the mobile ecosystem issometimes able to sacrifice overall performance for power savings. Yet,it's a singular purpose of most fabrics to provide highest possibleperformance with maximum power saving. Below, a number of interconnectsare discussed, which would potentially benefit from aspects of theinvention described herein.

One interconnect fabric architecture includes the Peripheral ComponentInterconnect (PCI) Express (PCIe) architecture. A primary goal of PCIeis to enable components and devices from different vendors tointer-operate in an open architecture, spanning multiple marketsegments; Clients (Desktops and Mobile), Servers (Standard andEnterprise), and Embedded and Communication devices. PCI Express is ahigh performance, general purpose I/O interconnect defined for a widevariety of future computing and communication platforms. Some PCIattributes, such as its usage model, load-store architecture, andsoftware interfaces, have been maintained through its revisions, whereasprevious parallel bus implementations have been replaced by a highlyscalable, fully serial interface. The more recent versions of PCIExpress take advantage of advances in point-to-point interconnects,Switch-based technology, and packetized protocol to deliver new levelsof performance and features. Power Management, Quality Of Service (QoS),Hot-Plug/Hot-Swap support, Data Integrity, and Error Handling are amongsome of the advanced features supported by PCI Express.

Referring to FIG. 1, an embodiment of a fabric composed ofpoint-to-point Links that interconnect a set of components isillustrated. System 100 includes processor 105 and system memory 110coupled to controller hub 115. Processor 105 includes any processingelement, such as a microprocessor, a host processor, an embeddedprocessor, a co-processor, or other processor. Processor 105 is coupledto controller hub 115 through front-side bus (FSB) 106. In oneembodiment, FSB 106 is a serial point-to-point interconnect as describedbelow. In another embodiment, link 106 includes a serial, differentialinterconnect architecture that is compliant with different interconnectstandard.

System memory 110 includes any memory device, such as random accessmemory (RAM), non-volatile (NV) memory, or other memory accessible bydevices in system 100. System memory 110 is coupled to controller hub115 through memory interface 116. Examples of a memory interface includea double-data rate (DDR) memory interface, a dual-channel DDR memoryinterface, and a dynamic RAM (DRAM) memory interface.

In one embodiment, controller hub 115 is a root hub, root complex, orroot controller in a Peripheral Component Interconnect Express (PCIe orPCIE) interconnection hierarchy. Examples of controller hub 115 includea chipset, a memory controller hub (MCH), a northbridge, an interconnectcontroller hub (ICH) a southbridge, and a root controller/hub. Often theterm chipset refers to two physically separate controller hubs, i.e. amemory controller hub (MCH) coupled to an interconnect controller hub(ICH). Note that current systems often include the MCH integrated withprocessor 105, while controller 115 is to communicate with I/O devices,in a similar manner as described below. In some embodiments,peer-to-peer routing is optionally supported through root complex 115.

Here, controller hub 115 is coupled to switch/bridge 120 through seriallink 119. Input/output modules 117 and 121, which may also be referredto as interfaces/ports 117 and 121, include/implement a layered protocolstack to provide communication between controller hub 115 and switch120. In one embodiment, multiple devices are capable of being coupled toswitch 120.

Switch/bridge 120 routes packets/messages from device 125 upstream, i.e.up a hierarchy towards a root complex, to controller hub 115 anddownstream, i.e. down a hierarchy away from a root controller, fromprocessor 105 or system memory 110 to device 125. Switch 120, in oneembodiment, is referred to as a logical assembly of multiple virtualPCI-to-PCI bridge devices. Device 125 includes any internal or externaldevice or component to be coupled to an electronic system, such as anI/O device, a Network Interface Controller (NIC), an add-in card, anaudio processor, a network processor, a hard-drive, a storage device, aCD/DVD ROM, a monitor, a printer, a mouse, a keyboard, a router, aportable storage device, a Firewire device, a Universal Serial Bus (USB)device, a scanner, and other input/output devices. Often in the PCIevernacular, such as device, is referred to as an endpoint. Although notspecifically shown, device 125 may include a PCIe to PCI/PCI-X bridge tosupport legacy or other version PCI devices. Endpoint devices in PCIeare often classified as legacy, PCIe, or root complex integratedendpoints.

Graphics accelerator 130 is also coupled to controller hub 115 throughserial link 132. In one embodiment, graphics accelerator 130 is coupledto an MCH, which is coupled to an ICH. Switch 120, and accordingly I/Odevice 125, is then coupled to the ICH. I/O modules 131 and 118 are alsoto implement a layered protocol stack to communicate between graphicsaccelerator 130 and controller hub 115. Similar to the MCH discussionabove, a graphics controller or the graphics accelerator 130 itself maybe integrated in processor 105.

Turning to FIG. 2 an embodiment of a layered protocol stack isillustrated. Layered protocol stack 200 includes any form of a layeredcommunication stack, such as a Quick Path Interconnect (QPI) stack, aPCIe stack, a next generation high performance computing interconnectstack, or other layered stack. Although the discussion immediately belowin reference to FIGS. 1-4 are in relation to a PCIe stack, the sameconcepts may be applied to other interconnect stacks. In one embodiment,protocol stack 200 is a PCIe protocol stack including transaction layer205, link layer 210, and physical layer 220. An interface, such asinterfaces 117, 118, 121, 122, 126, and 131 in FIG. 1, may berepresented as communication protocol stack 200. Representation as acommunication protocol stack may also be referred to as a module orinterface implementing/including a protocol stack.

PCI Express uses packets to communicate information between components.Packets are formed in the Transaction Layer 205 and Data Link Layer 210to carry the information from the transmitting component to thereceiving component. As the transmitted packets flow through the otherlayers, they are extended with additional information necessary tohandle packets at those layers. At the receiving side the reverseprocess occurs and packets get transformed from their Physical Layer 220representation to the Data Link Layer 210 representation and finally(for Transaction Layer Packets) to the form that can be processed by theTransaction Layer 205 of the receiving device.

Transaction Layer

In one embodiment, transaction layer 205 is to provide an interfacebetween a device's processing core and the interconnect architecture,such as data link layer 210 and physical layer 220. In this regard, aprimary responsibility of the transaction layer 205 is the assembly anddisassembly of packets (i.e., transaction layer packets, or TLPs). Thetranslation layer 205 typically manages credit-based flow control forTLPs. PCIe implements split transactions, i.e. transactions with requestand response separated by time, allowing a link to carry other trafficwhile the target device gathers data for the response.

In addition PCIe utilizes credit-based flow control. In this scheme, adevice advertises an initial amount of credit for each of the receivebuffers in Transaction Layer 205. An external device at the opposite endof the link, such as controller hub 115 in FIG. 1, counts the number ofcredits consumed by each TLP. A transaction may be transmitted if thetransaction does not exceed a credit limit. Upon receiving a response anamount of credit is restored. An advantage of a credit scheme is thatthe latency of credit return does not affect performance, provided thatthe credit limit is not encountered.

In one embodiment, four transaction address spaces include aconfiguration address space, a memory address space, an input/outputaddress space, and a message address space. Memory space transactionsinclude one or more of read requests and write requests to transfer datato/from a memory-mapped location. In one embodiment, memory spacetransactions are capable of using two different address formats, e.g., ashort address format, such as a 32-bit address, or a long addressformat, such as 64-bit address. Configuration space transactions areused to access configuration space of the PCIe devices. Transactions tothe configuration space include read requests and write requests.Message transactions are defined to support in-band communicationbetween PCIe agents.

Therefore, in one embodiment, transaction layer 205 assembles packetheader/payload 156. Format for current packet headers/payloads may befound in the PCIe specification at the PCIe specification website.

Quickly referring to FIG. 3, an embodiment of a PCIe transactiondescriptor is illustrated. In one embodiment, transaction descriptor 300is a mechanism for carrying transaction information. In this regard,transaction descriptor 300 supports identification of transactions in asystem. Other potential uses include tracking modifications of defaulttransaction ordering and association of transaction with channels.

Transaction descriptor 300 includes global identifier field 302,attributes field 304 and channel identifier field 306. In theillustrated example, global identifier field 302 is depicted comprisinglocal transaction identifier field 308 and source identifier field 310.In one embodiment, global transaction identifier 302 is unique for alloutstanding requests.

According to one implementation, local transaction identifier field 308is a field generated by a requesting agent, and it is unique for alloutstanding requests that require a completion for that requestingagent. Furthermore, in this example, source identifier 310 uniquelyidentifies the requestor agent within a PCIe hierarchy. Accordingly,together with source ID 310, local transaction identifier 308 fieldprovides global identification of a transaction within a hierarchydomain.

Attributes field 304 specifies characteristics and relationships of thetransaction. In this regard, attributes field 304 is potentially used toprovide additional information that allows modification of the defaulthandling of transactions. In one embodiment, attributes field 304includes priority field 312, reserved field 314, ordering field 316, andno-snoop field 318. Here, priority sub-field 312 may be modified by aninitiator to assign a priority to the transaction. Reserved attributefield 314 is left reserved for future, or vendor-defined usage. Possibleusage models using priority or security attributes may be implementedusing the reserved attribute field.

In this example, ordering attribute field 316 is used to supply optionalinformation conveying the type of ordering that may modify defaultordering rules. According to one example implementation, an orderingattribute of “0” denotes default ordering rules are to apply, wherein anordering attribute of “1” denotes relaxed ordering, wherein writes canpass writes in the same direction, and read completions can pass writesin the same direction. Snoop attribute field 318 is utilized todetermine if transactions are snooped. As shown, channel ID Field 306identifies a channel that a transaction is associated with.

Link Layer

Link layer 210, also referred to as data link layer 210, acts as anintermediate stage between transaction layer 205 and the physical layer220. In one embodiment, a responsibility of the data link layer 210 isproviding a reliable mechanism for exchanging Transaction Layer Packets(TLPs) between two components a link. One side of the Data Link Layer210 accepts TLPs assembled by the Transaction Layer 205, applies packetsequence identifier 211, i.e. an identification number or packet number,calculates and applies an error detection code, i.e. CRC 212, andsubmits the modified TLPs to the Physical Layer 220 for transmissionacross a physical to an external device.

Physical Layer

In one embodiment, physical layer 220 includes logical sub block 221 andelectrical sub-block 222 to physically transmit a packet to an externaldevice. Here, logical sub-block 221 is responsible for the “digital”functions of Physical Layer 221. In this regard, the logical sub-blockincludes a transmit section to prepare outgoing information fortransmission by physical sub-block 222, and a receiver section toidentify and prepare received information before passing it to the LinkLayer 210.

Physical block 222 includes a transmitter and a receiver. Thetransmitter is supplied by logical sub-block 221 with symbols, which thetransmitter serializes and transmits onto to an external device. Thereceiver is supplied with serialized symbols from an external device andtransforms the received signals into a bit-stream. The bit-stream isde-serialized and supplied to logical sub-block 221. In one embodiment,an 8b/10b transmission code is employed, where ten-bit symbols aretransmitted/received. Here, special symbols are used to frame a packetwith frames 223. In addition, in one example, the receiver also providesa symbol clock recovered from the incoming serial stream.

As stated above, although transaction layer 205, link layer 210, andphysical layer 220 are discussed in reference to a specific embodimentof a PCIe protocol stack, a layered protocol stack is not so limited. Infact, any layered protocol may be included/implemented. As an example,an port/interface that is represented as a layered protocol includes:(1) a first layer to assemble packets, i.e. a transaction layer; asecond layer to sequence packets, i.e. a link layer; and a third layerto transmit the packets, i.e. a physical layer. As a specific example, acommon standard interface (CSI) layered protocol is utilized.

Referring next to FIG. 4, an embodiment of a PCIe serial point to pointfabric is illustrated. Although an embodiment of a PCIe serialpoint-to-point link is illustrated, a serial point-to-point link is notso limited, as it includes any transmission path for transmitting serialdata. In the embodiment shown, a basic PCIe link includes two,low-voltage, differentially driven signal pairs: a transmit pair 406/411and a receive pair 412/407. Accordingly, device 405 includestransmission logic 406 to transmit data to device 410 and receivinglogic 407 to receive data from device 410. In other words, twotransmitting paths, i.e. paths 416 and 417, and two receiving paths,i.e. paths 418 and 419, are included in a PCIe link.

A transmission path refers to any path for transmitting data, such as atransmission line, a copper line, an optical line, a wirelesscommunication channel, an infrared communication link, or othercommunication path. A connection between two devices, such as device 405and device 410, is referred to as a link, such as link 415. A link maysupport one lane—each lane representing a set of differential signalpairs (one pair for transmission, one pair for reception). To scalebandwidth, a link may aggregate multiple lanes denoted by xN, where N isany supported Link width, such as 1, 2, 4, 8, 12, 16, 32, 64, or wider.

A differential pair refers to two transmission paths, such as lines 416and 417, to transmit differential signals. As an example, when line 416toggles from a low voltage level to a high voltage level, i.e. a risingedge, line 417 drives from a high logic level to a low logic level, i.e.a falling edge. Differential signals potentially demonstrate betterelectrical characteristics, such as better signal integrity, i.e.cross-coupling, voltage overshoot/undershoot, ringing, etc. This allowsfor better timing window, which enables faster transmission frequencies.

New and growing use models, such as PCIe-based storage arrays andThunderbolt, are driving a significant increase in PCIe hierarchy depthand width. The PCI Express (PCIe) architecture was based on PCI, whichdefines a “Configuration Space” in which system firmware and/or softwarediscover Functions and enable/disable/control them. The addressingwithin this space is based on a 16 bit address (commonly referred to asthe “BDF”, or bus-device-function number) consisting of an 8 bit BusNumber, a 5 bit Device Number, and a 3 bit Function Number. In PCIe theBus Number can refer to a logical, rather than a physical bus. Inaddition to being used for to address PCI Functions in Configurationspace, and to identify specific Functions for purposes such as errorreporting and IO Virtualization, the space, itself, can be considered atype of resource which is subject to issues of allocation and managementsimilar to other resources.

PCI allows systems to provide for multiple, independent BDF spaces,which are called “Segments”. Each Segment may have certain resourcerequirements, such as a mechanism for generating PCI/PCIe ConfigurationRequests, including the Enhanced Configuration Access Mechanism (ECAM)defined in the PCIe specification. Additionally, input/output (I/O)memory management units (IOMMUs) (such as Intel VT-d) can use BDF spaceas an index, but may not be configured to directly comprehend Segments.Accordingly, in some instances, a separate ECAM and IOMMU is duplicatedfor each Segment defined in a system. FIG. 5 illustrates an example of asystem including multiple segments (e.g., 505 a-c). For instance, aSegment, in this example, is defined for each one of three switches 510,515, 520 that connect to a Root Complex 525. In this example, a separateIOMMU and ECAM (e.g., 530 a-c) can be implemented at the Root Complex525 to facilitate each of the Segments (e.g., 505 a-c). Further, in thisexample, a variety of endpoints (EP) are connected to various buses ineach Segment. In some cases, configuration space of a Segment mayreserve multiple bus addresses for potential hot plug events, limitingthe total number of bus addresses that are available within eachSegment. Still further, allocation of bus numbers in one or more of theSegments may be according to an algorithm that concerns itself littlewith densely populating the addresses and making compact use of theavailable bus address space. This can result in wasted configurationaddress (i.e., BDF) space in some instances.

Traditional PCIe systems are configured to assign address space in amanner that, when applied to modern and emerging use cases, tends tomake inefficient use of BDF space and of Bus Numbers in particular.While relatively few implementations may actually involve a singlesystem consuming all 64K of unique BDF values (e.g., defined underPCIe), deep hierarchies such as those that occur, for example, in deephierarchies of PCIe Switches, may use up available Bus Numbers veryquickly. Additionally, in applications supporting hot plugging, largeportions of the BDF space may be typically reserved for future potentialuse (i.e., when a future device is hot plugged to the system), takingadditional swaths of Bus Numbers from the pool immediately usable by asystem. While Segment mechanisms can be applied to address this issue,Segments themselves have poor scaling because, as noted above,additional hardware resources (e.g., IOMMUs) are to be built into theCPU, platform controller hub (PCH), system on chip (SoC), root complex,etc., in order to support each segment. Thus using Segments to addressdeep hierarchies results in scaling the system to satisfy a worst casesystem requirement, which is typically much more than what would beneeded for most systems, resulting in significant waste of platformresources. Further, Segments can be difficult (and, in some cases,essentially impossible) to create outside of a root complex of thesystem.

In some implementations, a system can be provided to enable moreefficient use of BDF space and address at least some of the exampleissues above. This can allow for the expansion of PCIe, Thunderbolt,system on chip fabrics (e.g., Intel On-Chip System Fabric (IOSF) andothers), and other interconnects to very large topologies, but withoutrequiring dedicated resources in the Root Complex, as would be the casein solutions relying exclusively on Segments or other alternatives. FIG.6 illustrates an example assignment of bus numbers to buses within thesystem according to an example PCIe BDF assignment. In this example, asystem with two devices 605, 610 directly connected to a Root Complex615 and two Switch-based hierarchies (corresponding to switches 620,625) are enumerated with approximately the densest possible Bus Numberallocations using conventional BDF assignment (as designated by circlelabels (e.g., 650 a-d, etc.)). In deep hierarchies, the available busnumbers in a single BDF space can be quickly consumed. Further, realworld systems typically allocate bus numbers far less efficiently,resulting in sparse (or “wasted”) allocation of the BDF space.

Another problem with use cases that support hot add/remove such asThunderbolt and, in some cases, PCIe-based storage, is that the BusNumber assignments in BDF space are “rebalanced” to address hardwaretopology changes occurring in a running system. Rebalancing, however,can be very difficult for system software to do because, in typicalcases, all PCI Functions are then forced into a quiescent state inconnection with the rebalancing in order to allow the BDF space to bere-enumerated by the system, followed by the re-enabling of the PCIFunctions. This process can be quite slow, however, and typicallyresults in the system freezing for what can be very long periods of time(e.g., long enough to be disruptive to running applications, and visibleto the end user). An improved system can also be provided to shorten thetime it takes to apply a revised BDF space such that the rebalancingprocess can be performed in a span of hundredths of milliseconds orquicker and without explicitly placing PCI Functions into quiescentstates. Finally, very large systems or systems with (proprietary)mechanisms for supporting multiple Root Complexes, may be defined torequire the use of Segments.

As introduced above, the Flattening Portal Bridge (FPB) can be anoptional mechanism which can be used to address at least some of theexample issues above, including improving the scalability and runtimereallocation of Bus/Device/Function (BDF) and Memory-Mapped IO (MMIO)spaces. The concept of “BDF space” is related to the ConfigurationAddress Space, but is generalized to recognize that the BDF is the basisfor the Requester and Completer IDs, the routing of completions, and canserve as an essential element in several mechanisms in addition to therouting of Configuration Requests. For Functions associated with anUpstream Port, the Function Number portion of the BDF space address(e.g., 3-bit Function Number) may be determined by the construction ofthe Upstream Port hardware, whereas the Bus and Device Number portionsmay be determined by the Downstream Port above the Upstream Port. Anexample FPB may maintain the existing architecture where the UpstreamPort determines the mapping of Functions within the 3 bit FunctionNumber portion of the BDF, and operates only within the 13 bitBus/Device Number portion. In such instances, “BD Space” may refer tothe 13 bit Bus/Device Number portion of the BDF. MMIO here can referspecifically to Memory Read and Write Requests that pass through a RootPort, Switch Port, or logical Bridge where the FPB capability providesadditional mechanisms to determine the address decoding of suchrequests. A Bridge that implements the FPB capability can itself also bereferred to as an FPB.

FIG. 7A is a simplified block diagram illustrating the provision of FPBlogic at each port of one or more switches within a system. Someswitches may not include FPB logic and only support bus enumerationaccording to conventional BDF or MMIO space assignments. Moreover, portsof a root complex 705 may also include FPB logic, such as ports designedto potentially support dynamic cases hot plugging or flexibly supportvaried architecture (e.g., not predefined at design time of the rootcomplex), among other examples. Further, some ports of the root complex705, may omit FPB logic, such as ports designed to support static cases,such as ports connected to endpoints 710, 715, in the example of FIG.7A, among other examples.

FPB logic can be enabled or disabled at each port possessing the FPBlogic. FPB logic can be implemented in hardware, firmware, and/orsoftware to support the assignment of BDF or MMIO space using a“flattened” approach. For example, each bus interconnecting switches,endpoints, and the root complex can be assigned a unique bus number(e.g., as discussed in connection with FIG. 6), with a number of devicescapable of being addressed by a respective one of 32 possible devicenumbers under each bus number, and a number of possible functionsnumbers capable of being addressed by a respective one of 8 possiblefunction numbers under each device number. Flattening through FPB canallow at least some of the buses to be addressed uniquely by abus-device (BD) number combination (rather than by a unique bus number),extending the maximum number of unique potential bus addresses from 256(under traditional PCIe bus number enumeration) to 8192 (under BD busenumeration). As a consequence, under FPB, the bus number can be re-usedfor several different buses, albeit with each bus number having a uniqueBD number (i.e., the bus number portion of the BD being the same but thedevice number under that bus number being different). Some branches ofthe system can utilize conventional bus addressing (e.g., by BDF busnumber), while other branches utilize FPB-based addressing. Indeed, amix of bus enumeration schemes can be employed, with the resultremaining unique bus addresses being employed within the system.

Turning to FIG. 7B is a simplified block diagram illustrating a highlevel architecture of an example implementation of a FPB logic block(such as illustrated at ports shown in the example of FIG. 7A). A type 1bridge function can be provided through each FPB module. The bridgefunction can support both legacy packet decode/routing mechanisms (e.g.,conventional PCIe BDF decoding and routing) as well as FPB packetdecode/routing mechanisms.

FPB changes the way BDF resources are consumed by Switches to reducewaste, by “flattening” the way Bus Numbers are used inside of Switchesand by Downstream Ports. FPB defines mechanisms for system software toallocate BDF and MMIO resources in non-contiguous ranges, enablingsystem software to assign pools of BDF/MMIO from which it can allocate“bins” to Functions below the FPB. This allows system software to assignBDF/MMIO required by a device hot-add without having to rebalance other,already assigned resource ranges, and to return to the pool resourcesfreed, for example, by a hot remove event. FPB is defined to allow thelegacy and new mechanisms to operate simultaneously, such that, forexample, it is possible for system firmware/software to implement apolicy where the legacy mechanisms continue to be used in parts of thesystem where the FPB mechanisms may not be required. In the example ofFIG. 7B, the decode logic may be assumed to provide a ‘1’ output when agiven TLP is decoded as being associated with the bridge's SecondarySide. The legacy decode mechanisms may apply as before, so for exampleonly the Bus Number portion (bits 15:8) of a BDF address may be testedby the legacy BDF decode logic, among other examples.

As illustrated in the example of FIG. 8, an instance of FPB logic caninclude both legacy packet decode/routing mechanisms and FPB packetdecode/routing mechanisms. For legacy packet decode/routing mechanisms.A TLP can be identified at the FPB-provisioned port and legacy packetdecode/routing mechanisms can determine whether to route the TLP to thesecondary side of the port or to keep the TLP routing at the primaryside, based on conventional BDF routing. Likewise, the FPB packetdecode/routing mechanism can determine whether to route the TLP to thesecondary side of the port or to keep the TLP routing at the primaryside, based on flattened BDF routing. If either the legacy packetdecode/routing mechanisms or the FPB packet decode/routing mechanismsoutput an indication that the packet should proceed to the secondaryside, routing of the packet traverses the bridge to the secondary sidefor routing to its destination. Legacy packet decode/routing mechanismscan include, for BDF decode, secondary/subordinate bus number registersand, for memory (e.g., MMIO) decode, memory base/limit registers,prefetchable base/limit registers, a VGA enable bit, enhancedallocation, among other mechanisms usable by the FPB logic. FPB packetdecode/routing mechanisms can include, for BD space decode, BD secondarystart, vector start, granularity, and related registers, for use inconnection with the BD vector. Memory decode can also utilize vectors inFPB, such as a MEM Low Vector for use in connection with MEM Low VectorStart, Granularity, and related MEM Low registers and a MEM High Vectorfor use in connection with MEM High Vector Start, Granularity, andrelated MEM High registers, among other example registers, mechanisms,functionality, and features.

In some cases, although FPB may add additional ways for a specificBridge to decode a given TLP, FPB may not change anything about thefundamental ways that Bridges operate within the Switch and Root Complexarchitectural structures. In one example, FPB uses the samearchitectural concepts to provide management mechanisms for threedifferent resource types: the Bus/Device space, bits 15:3, of BDF(“BD”); Memory below 4 GB (“MEM Low”); and Memory above 4 GB (“MEMHigh”). A hardware implementation of FPB is permitted to support anycombination of these three mechanisms. For each mechanism, FPB uses abit-vector to indicate, for a specific subset range of the selectedresource type, if resources within that range are associated with thePrimary or Secondary side of the FPB. Hardware implementations can bepermitted to implement a small range of sizes for these vectors, andsystem firmware/software is enabled to make the most effective use ofthe available vector by selecting an initial offset at which the vectoris applied in increasing BD/Address order, and a granularity for theindividual bits within the vector to indicate the size of the BD/Addressresource set to which the bits in a given vector apply.

For each of the BD/Mem Low/Mem High mechanisms, it may be desirable,especially for a Root Complex, to provide a mechanism, e.g.configuration registers, by which hardware or system-specificfirmware/software can constrain the permissible range of BD/MMIO thatsystem software is allowed to assign to the Secondary Side of a RootPort bridge. This may simplify the construction of multi-component RootComplexes, for example, by ensuring that system software will notattempt to apply FPB mechanisms to overlapping ranges of BD/MMIO spacebetween Root Ports implemented on different components of themulti-component Root Complex, for example so that the Root Ports on onecomponent are permitted to work within a given range of BD/MMIOresources, and the Root Ports on another component are permitted to workwithin a different, non-overlapping with the first range, of BD/MMIOresources, among other examples.

In the static use cases (or simply “static cases”) there are limits onthe size of hierarchies and number of endpoints due to the Bus andDevice number “waste” caused by the PCI/PCIe architectural definitionfor Switches, and by the traditional requirement that Downstream Portsassociate an entire Bus Number with their Link. In some implementations,this class of problems can be addressed by “flattening” the use of BDFspace so that Switches and Downstream Ports are able to make moreefficient use of the available space. For Dynamic use cases (or simply“Dynamic cases”), rebalancing has been avoided by reserving large rangesof Bus Numbers and memory-mapped I/O (MMIO) in the Bridge above therelevant Endpoint(s) to attempt to satisfy any needs within thepre-allocated ranges. This approach, however, leads to additional waste,which amplifies the shortcomings of traditional BDF allocation.Moreover, this approach can be difficult to implement in the generalcase, even for relatively simple cases, where, for example, one mighthave a solid-state drive (SSD) implementing a single Endpoint replacedby a unit that has a Switch, creating an internal hierarchy within theunit, so that although an initial allocation of just one Bus would havebeen sufficient, the initial allocation breaks immediately with the newunit. Further, for MMIO the pre-allocation approach can be problematicwhen hot-plugged Endpoints may require the allocation of MMIO spacebelow 4 GB (by its nature a limited resource), which is quickly used upby pre-allocation of even relatively small amounts, and for whichpre-allocation is unattractive because of the multiple system elementsplacing demands on system address space allocation below 4 GB. Dependingon multiple factors including a given system's physical memoryaddressing capability, there may, in some cases, also be resourceconstraints in MMIO space above 4 GB. The constraints that apply to MMIOspace below 4 GB may differ from those that apply above 4 GB(accordingly separate mechanisms may be optimized for each).

In some implementations, at least some of the issues in both the Staticand Dynamic use cases can be addressed by defining mechanisms to enablediscontinuous resource range (re/)allocation for both BDF and MMIO.System software can possess the ability to maintain resource “pools,”which can be allocated (and freed back to) at run-time, withoutdisrupting other operations in progress as is required with rebalancing.A Flattening Portal Bridge (FPB) can thereby be provided as an optionalCapability that may be implemented by Type 1 (Bridge) Functions in Rootand Switch Ports to support more efficient and dense BDF allocation, toenable reallocation of BDF resources without requiring the rebalancingof resources assigned elsewhere in a system, and to enable discontiguousMMIO regions and avoid the need to rebalance MMIO resources. IO spaceallocation, in some implementations, may be left as-is and not modifiedby FPB. Among the potential example advantages provided by an exampleFPB, BDF space allocation can be more efficient and dense enablinglarger hierarchies, runtime reallocation of resources can be enabled forhot add/remove cases without the need to globally rebalance resources,the requirement for BDFs and MMIO to be allocated in contiguous rangescan be retired, mixed systems can be supported including components thatsupport FPB along with components that do not, all while permitting nochanges to existing Discrete Endpoints. For instance, legacy rootcomplexes, Switches, Bridges and Endpoints can be used in mixed systemenvironments along with RCs and Switches implementing FPB.

In some implementations, FPB can include the provisioning of newhardware and software supporting the FPB. This additional hardwareand/or software, however, can be optionally enabled in that it has noeffect unless enabled, and is disabled by default. In some instances,hardware changes to implement FPB can include hardware involving Type 1functions, while allowing Endpoints and hardware supporting Type 0functions to remain unaffected. FPB-enabled hardware can pass existingcompliance and interoperability tests and new tests can be developed toexplicitly evaluate the additional FPB functionality. Software intendingto work with devices implementing the FPB functionality can beconfigured to comprehend the new extended capability. Legacy softwarewill continue to function with FPB hardware, but will not be able tomake use of the FPB features.

FPB can continue to allow the use of legacy resource allocationmechanisms for BDF and MMIO. In some cases it may be desirable to havesystem firmware continue to perform the initial system resourceallocation using only the legacy mechanisms, and only use FPB after theoperating system has booted. FPB may support this and specificallyenable the system to continue to use the resources as allocated by thelegacy mechanisms. FPB is specifically intended to enable systemsoftware to modify the resource allocation within the system duringruntime requiring only that the hardware and processes associated withthe resources being modified be made quiescent, and allowing all otherhardware and processes to continue normal operation.

To support the runtime use of FPB by system software, FPB hardwareimplementations should avoid introducing stalls or other types ofdisruptions to transactions in flight, including during the times thatsystem software is modifying the state of the FPB hardware. It is not,however, expected that hardware will attempt to identify cases wheresystem software erroneously modifies the FPB configuration in a way thatdoes affect transactions in flight. Just as with the legacy mechanisms,it is the responsibility of system software to ensure that systemoperation is not corrupted due to a reconfiguration operation. It is notexplicitly required that system firmware/software perform the enablingand/or disabling of FPB mechanisms in a particular sequence, howeverrules can be defined to implement resource allocation operations in ahierarchy such that the hardware and software elements of the system arenot corrupted or caused to fail.

In some implementations, if system software violates any of the rulesconcerning FPB, the hardware behavior can be undefined. FPB can beimplemented in any PCI Bridge (Type 1) Function, and every Function thatimplements FPB implements the FPB Extended Capability. If a Switchimplements FPB then the Upstream Port and all Downstream Ports of theSwitch implement FPB. A Root Complex may be permitted to implement FPBon some Root Ports but not on others. A Root Complex may be permitted toimplement FPB on an internal logical bus of the Root Complex. A Type 1Function is permitted to implement the FPB mechanisms applying to anyone, two or three of these elemental mechanisms (BD, MEM Low, MEM High).System software may be permitted to enable any combination (includingall or none) of the elemental mechanisms supported by a specific FPB.The error handling and reporting mechanisms, except where explicitlymodified in this section, may be unaffected by FPB. In the event of areset of an FPB Function, the FPB hardware Clears all bits in allimplemented vectors. Once enabled (e.g., through the FPB BD VectorEnable, FPB MEM Low Vector Enable, and/or FPB MEM High Vector Enablebits), if system software subsequently disables an FPB mechanism, thevalues of the entries in the associated vector are undefined, and ifsystem software subsequently re-enables that FPB mechanism the FPBhardware Clears all bits in the associated vector.

In some implementations, system software is expressly permitted tomodify an FPB vector when the corresponding FPB mechanism is enabled. Ifan FPB is implemented with the No_Soft_Reset bit Clear, when that FPB iscycled through D0→D3hot→D0, then, as with other Function ConfigurationContext, all FPB mechanisms are to be disabled, and the FPB clears allbits in all implemented vectors. If an FPB is implemented with theNo_Soft_Reset bit Set, when that FPB is cycled through D0→D3hot→D0,then, as with other Function Configuration Context, all FPBconfiguration states do not change and the entries in the FPB vectorsare retained by hardware. Hardware can be implemented such that norequirement exists for performing any type of bounds checking on FPBcalculations, and system software can ensure that the FPB parameters arecorrectly programmed. For instance, a system software can be permittedto program Vector Start values that cause the higher order bits of thecorresponding vector to surpass the resource range associated with agiven FPB, with system software ensuring that those higher order bits ofthe vector are Clear. Examples of errors that system software must avoidinclude duplication of resource allocation, combinations of startoffsets with set vector bits that could create “wrap-around” or boundserrors, among other examples.

In some implementations of the FPB BD mechanism, FPB hardware considersa specific BDF to be associated with the Secondary side of the FPB ifthat BDF falls within the Bus Number range indicated by the valuesprogrammed in the Secondary and Subordinate Bus Number registerslogically OR′d with the value programmed into the corresponding entry inthe BD Vector. When using only the FPB BD mechanism for BDF decoding,system software can be utilized to ensure that both the Secondary andSubordinate Bus Number registers are 0. System software can furtherensure that the FPB routing mechanisms are configured such thatConfiguration Requests targeting Functions Secondary side of the FPBwill be routed by the FPB from the Primary to Secondary side of the FPB.The FPB BD mechanism can be applied with different granularities,programmable by system software through the FPB BD Vector Granularityregister in the FPB BD Vector Control 1 Register. For instance, FIG. 9illustrates example addresses in BDF space and supported granularities.The representation in FIG. 9 illustrate relationships between the layoutof addresses in BDF space and the supported granularities.

In some implementations, system software programs the FPB BD VectorGranularity and FPB BD Vector Start fields in the FPB BD Vector Control1 register per the constraints described in the descriptions of thosefields. The FPBs (other than those associated with Upstream Ports ofSwitches) may be constrained such that when PCIe Alternative Routing IDInterpretation (ARI) Forwarding is not supported, or when the ARIForwarding Enable bit in the Device Control 2 register is Clear, FPBhardware is to convert a Type 1 Configuration Request received on thePrimary side of the FPB to a Type 0 Configuration Request on theSecondary side of the FPB when the BD address (bits 15:3 of the BDF) ofthe Type 1 Configuration Request matches the value in the BD SecondaryStart field in the FPB BD Vector Control 2 Register, and system softwaremust configure the FPB accordingly. When the ARI Forwarding Enable bitin the Device Control 2 register is Set, FPB hardware converts a Type 1Configuration Request received on the Primary side of the FPB to a Type0 Configuration Request on the Secondary side of the FPB when the BusNumber address (bits 15:8 of the BDF) of the Type 1 ConfigurationRequest matches the value in the Bus Number address (bits 15:8 only) ofthe Secondary Start field in the FPB BD Vector Control 2 Register, andsystem software must configure the FPB accordingly.

In some implementations, for FPBs associated with Upstream Ports ofSwitches only, FPB hardware can use the FPB Num Sec Dev field of the FPBCapability Register to indicate the quantity of Device Numbersassociated with the Secondary Side of the Upstream Port Bridge, whichcan be used by the FPB in addition to the BD Secondary Start field inthe FPB BD Vector Control 2 Register to determine when a ConfigurationRequest received on the Primary side of the FPB targets one of theDownstream Ports of the Switch, determining in effect when such aRequest is to be converted form a Type 1 Configuration Request to a Type0 Configuration Request, with system software configuring the FPBappropriately. If ACS Source Validation is enabled at a Downstream Port,the FPB checks the Requester ID of each Upstream Request received by thePort to determine if it is mapped to the Secondary side of the FPB, andif the Requester ID is not then this can constitute a reported error(e.g., ACS Violation) associated with the Receiving Port. FPBs canfurther implement bridge mapping for INTx virtual wires.

In one example, to determine which entry in the FPB BD Vector applies toa given BDF address, FPB-provisioned hardware and software can apply analgorithm such as:

// “BDF” is the BDF address to be tested IF (BDF <= FPB_BD_Vector_Start)THEN  EXIT; // In this case the BDF is out of range // Otherwise, applyStarting offset OffsetIndex := BDF − FPB_BD_Vector_Start; // Next adjustfor the granularity of the vector // (this operation is a divide, donehere // as a right shift with zero fill) OI_Gran_Adjusted := ShiftRightZeroFill(FPB_BD_Vector_Granularity,    Offset Index); IF(OI_Gran_Adjusted >= LENGTHOF(FPB BD Vector)) THEN  EXIT; // In thiscase the BDF is out of range // Otherwise, locate the bit in the (bitaddressed) vector SelectorBit := FPB_BD_Vector[OI Gran Adjusted_9 ; //If SelectorBit is Set, then the BDF is considered to be // on theSecondary Side, if Clear, the BDF is // considered to be on the PrimarySide.

In other words, to determine which entry in the FPB BD Vector applies toa given BDF address, logic may determine if the BD address is below thevalue of FPB BD Vector Start. If the BD address is below, then the BD isout of range and is not to be associated with the Secondary side of thebridge. Otherwise, the logic may calculate the offset within the vectorby first subtracting the value of FPB BD Vector Start, then dividingthis according to the value of FPB BD Vector Granularity to determinethe bit index within the vector. If the bit index value is greater thanthe length indicated by FPB BD Vector Size Supported, then the BD is outof range (above) and is not to be associated with the Secondary side ofthe bridge. However, if the bit value within the vector at thecalculated bit index location is 1b, then the BD address is associatedwith the Secondary side of the bridge, otherwise the BD address isassociated with the Primary side of the bridge.

The FPB MEM Low mechanism can be applied with different granularities,programmable by system software through the FPB MEM Low VectorGranularity register in the FPB MEM Low Vector Control Register. FIG. 10illustrates the layout of addresses in the memory address space below 4GB to which the FPB MEM Low mechanism applies and the effect ofgranularity on these addresses. FIG. 10 also relates to the definitionof the Flattening Portal Bridge (FPB) Extended Capability. Systemsoftware can program the FPB MEM Low Vector Granularity and FPB MEM LowVector Start fields in the FPB MEM Low Vector Control register per theconstraints described in the descriptions of those fields.

In instances of the FPB MEM Low mechanism, FPB hardware can consider aspecific Memory address to be associated with the Secondary side of theFPB if that Memory address falls within any of the ranges indicated bythe values programmed in other Bridge Memory decode registers(enumerated below) logically OR'd with the value programmed into thecorresponding entry in the MEM Low Vector. Other Bridge Memory decoderegisters can include: Memory Base/Limit registers in the Type 1(Bridge) header; Prefetchable Base/Limit registers in the Type 1(Bridge) header; VGA Enable bit in the Bridge Control Register of theType 1 (Bridge) header; Enhanced Allocation (EA) Capability; FPB MEMHigh mechanism (if supported and enabled). In one example, to determinewhich entry in the FPB MEM Low Vector applies to a given Memory address,hardware and software can apply an algorithm such as:

// “Address” is the memory address to be tested // expressed in MB units(i.e. bits [31:20] ) IF (Address <= FPB_MEM_Low_Vector_Start) THEN EXIT; // In this case the address is out of range // Otherwise, applyStarting offset OffsetIndex := Address − FPB_MEM_Low_Vector_Start; //Next adjust for the granularity of the vector // (this operation is adivide, done here // as a right shift with zero fill) OI_Gran_Adjusted:=  ShiftRightZeroFill(FPB_MEM_Low_Vector_Granularity,    Offset Index);IF (OI_Gran_Adjusted >=   LENGTHOF (FPB_MEM_Low_Vector)) THEN  EXIT; //In this case the address is out of range // Otherwise, locate the bit inthe (bit addressed) vector SelectorBit :=FPB_MEM_Low_Vector[OI_Gran_Adjusted]; // If SelectorBit is Set, then theaddress is // considered to be on the Secondary Side, // if Clear, theaddress is considered to be on // the Primary Side.

In other words, to determine which entry in the FPB MEM Low Vectorapplies to a given Memory address, hardware and software can determineif the Memory address is below the value of FPB MEM Low Vector Start. Ifso, the Memory address may is out of range (below) and is not associatedwith the Secondary side of the bridge. The logic may calculate theoffset within the vector by first subtracting the value of FPB MEM LowVector Start, then dividing this according to the value of FPB MEM LowVector Granularity to determine the bit index within the vector. If thebit index value is greater than the length indicated by FPB MEM LowVector Size Supported, then the Memory address is out of range (above)and is not to be associated with the Secondary side of the bridge. Onthe other hand, if the bit value within the vector at the calculated bitindex location is 1b, then the Memory address may be associated with theSecondary side of the bridge, otherwise the Memory address is associatedwith the Primary side of the bridge.

System software can program the FPB MEM High Vector Granularity and FPBMEM High Vector Start Lower fields in the FPB MEM High Vector Control 1register per the constraints described in the descriptions of thosefield. In instances of the FPB MEM High mechanism, FPB hardware canconsider a specific Memory address to be associated with the Secondaryside of the FPB if that Memory address falls within any of the rangesindicated by the values programmed in other Bridge Memory decoderegisters (enumerated below) logically OR'd with the value programmedinto the corresponding entry in the MEM Low Vector. Other Bridge Memorydecode registers can include Memory Base/Limit registers in the Type 1(Bridge) header; Prefetchable Base/Limit registers in the Type 1(Bridge) header; VGA Enable bit in the Bridge Control Register of theType 1 (Bridge) header; Enhanced Allocation (EA) Capability; and FPB MEMLow mechanism (if supported and enabled). In one example, to determinewhich entry in the FPB MEM High Vector applies to a given Memoryaddress, hardware and software can apply an algorithm such as:

// “Address” is the memory address to be tested // expressed in 16MBunits (i.e. bits [63:24]) // “FPB_MEM_High_Vector_Start” is theconcatenation // of FPB MEM High Vector Start Upper and // FPB MEM HighVector Start Lower IF (Address <= FPB_MEM_High_Vector_Start) THEN  EXIT;// In this case the address is out of range // Otherwise, apply Startingoffset OffsetIndex := Address − FPB_MEM_High_Vector_Start; // Nextadjust for the granularity of the vector // (this operation is a divide,shown here // as a right shift with zero fill) // We have to apply anadditional shift of 4 bits // to account for the granularity unitsOI_Gran_Adjusted :=  ShiftRightZeroFill(  ShiftRightZeroFill(FPB_MEM_High_Vector_Granularity,    OffsetIndex),4); IF (OI_Gran_Adjusted >=   LENGTHOF(FPB_MEM_High_Vector)) THEN  EXIT;// In this case the address is out of range // Otherwise, locate the bitin the (bit addressed) vector SelectorBit :=FPB_MEM_High_Vector[OI_Gran_Adjusted]; // If SelectorBit is Set, thenthe address is // considered to be on the Secondary Side, // if Clear,the address is considered to be on // the Primary Side.

In other words, to determine which entry in the FPB MEM High Vectorapplies to a given Memory address, hardware and software can determineif the Memory address is below the value of FPB MEM High Vector Start.If so, the Memory address can be determined to be out of range (below)and is not associated with the Secondary side of the bridge. Otherwise,the offset within the vector can be calculated by first subtracting thevalue of FPB MEM High Vector Start, then dividing this according to thevalue of FPB MEM High Vector Granularity to determine the bit indexwithin the vector by means of this mechanism. If the bit index value isgreater than the length indicated by FPB MEM High Vector Size Supported,then the Memory address is out of range (above) and so is not associatedwith the Secondary side of the bridge. Otherwise, if the bit valuewithin the vector at the calculated bit index location is 1b, then theMemory address is associated with the Secondary side of the bridge, orthe Memory address is associated with the Primary side of the bridge.

In some implementations, FPB may use a bit vector mechanism to describeaddress spaces (BD Space, MEM Lo, & Mem Hi). A bridge supporting FPB maycontain the following for each address space where it supports the useof FPB: a Bit vector; a Start Address register; and a Granularityregister. These values may be used by the bridge to determine if a givenaddress is part of the range decoded by FPB as associated with thesecondary side of the bridge. An address that is not determined to beassociated with the secondary side of the bridge using either or both ofthe legacy decode mechanisms and the FPB decode mechanisms is (bydefault) associated with the primary side of the bridge. Here, the term“associated” may mean, for example, that the bridge will apply thefollowing handling to TLPs:

-   -   A TLP associated with the Primary side and received at the        Primary side may be handled as an Unsupported Request (UR);    -   A TLP associated with the Primary and received at the Secondary        side may be handled as a Forward upstream;    -   A TLP associated with the Secondary side and received at the        Primary side may be handled as a Forward downstream;    -   A TLP associated with the Secondary side and received at the        Secondary side may be handled as a Unsupported Request (UR),        etc.        In FPB, every bit in the vector may represents a range of        addresses, where the size of that range is determined by the        selected granularity. If a bit in the vector is Set, it        indicates that packets addressed to an address within the        corresponding range are to be associated with the secondary side        of the bridge. The specific range of addresses each bit        represents is dependent on the index of that bit, and the values        in the Start Address & Granularity registers. The Start Address        register indicates the lowest address described by the bit        vector. The Granularity register indicates the size of the        region that is represented by each bit. Each successive bit in        the vector applies to the subsequent range, increasing with each        bit according to the Granularity.

In some cases, Downstream Ports that do not have ARI Forwarding enabledare to associate only Device 0 with the device attached to the LogicalBus representing the Link from the Port. Configuration Requeststargeting the Bus Number associated with a Link specifying Device Number0 are delivered to the device attached to the Link. ConfigurationRequests specifying all other Device Numbers (1-31) may thus beterminated by the Switch Downstream Port or the Root Port with anUnsupported Request Completion Status (equivalent to Master Abort inPCI). In some cases, non-ARI Devices may not assume that Device Number 0is associated with their Upstream Port, but will instead capture theirassigned Device Number and respond to all Type 0 Configuration ReadRequests, regardless of the Device Number specified in the Request. Insome examples, when an ARI Device is targeted and the Downstream Portimmediately above it is enabled for ARI Forwarding, the Device Number isimplied to be 0, and the traditional Device Number field is used insteadas part of an 8-bit Function Number field. If Configuration Request Typeis 1, FPB logic can determine if the Bus Number and Device number fieldsare (in the case of a PCI Express-PCI Bridge) equal to the Bus Numberassigned to secondary PCI bus or, in the case of a Switch or RootComplex, equal to the Bus Number and decoded Device Numbers assigned toone of the Root (Root Complex) or Downstream Ports (Switch). If so, theRequest may be forwarded to that Downstream Port (or PCI bus, in thecase of a PCI Express-PCI Bridge). If not equal to the Bus Number of anyof Downstream Ports or secondary PCI bus, but in the range of BusNumbers assigned to either a Downstream Port or a secondary PCI bus, theRequest can be forwarded to that Downstream Port interface withoutmodification.

The Flattening Portal Bridge (FPB) Extended Capability may be anoptional Extended Capability that is to be provided for any BridgeFunction or Port that implements FPB. If a Switch implements FPB thenthe Upstream Port and all Downstream Ports of the Switch implement theFPB Extended Capability Structure. A Root Complex is permitted toimplement the FPB Extended Capability Structure on some Root Ports butnot on others. A Root Complex may be permitted to implement the FPBCapability for internal logical busses in some implementations. In thefollowing description, the FPB registers are accessed by means of a PCIeExtended Capability, but in other example implementations the FPBregisters can be accessed through other means including but not limitedto a PCI capability structure, or a vendor-defined extended capability.The registers, in some implementations, can be hosted in memory elementsof the corresponding switches, bridges, root complex, or other deviceswithin the system.

Table 1 illustrates one example implementation of an FPB ExtendedCapability Header. In one example, the FPB Extended Capability Headercan have an offset of ooh.

TABLE 1 FPB Extended Capability Header Bit Location Register Description15:0 PCI Express Extended Capability ID-This field identifies thefollowing structure as an Extended Capability structure for a FlatteningPortal Bridge (FPB) 19:16 Capability Version-This field is a PCI-SIGdefined version number that indicates the version of the Capabilitystructure present. Must be 1h for this version of the specification.31:20 Next Capability Offset-This field contains the offset to the nextPCI Express Capability structure or 000h if no other items exist in thelinked list of Capabilities. For Extended Capabilities implemented inConfiguration Space, this offset is relative to the beginning of PCIcompatible Configuration Space and thus must always be either 000h (forterminating list of Capabilities) or greater than OFFh.

Table 2 illustrates one example implementation of an FPB CapabilityHeader. In one example, the FPB Capability Header can have an offset of04h.

TABLE 2 FPB Capability Register Bit Location Register Description 0 FPBBD Vector Supported-If Set, indicates that the BD Vector mechanism issupported. 1 FPB MEM Low Vector Supported-If Set, indicates that the MEMLow Vector mechanism is supported. 2 FPB MEM High Vector Supported-IfSet, indicates that the Mem High mechanism is supported. 7:3 FPB Num SecDev-For Upstream Ports of Switches only, this field indicates thequantity of Device Numbers associated with the Secondary Side of theUpstream Port Bridge. The quantity is determined by adding one to thenumerical value of this field. Although it is encouraged that Switchimplementations consume Function Numbers efficiently, it is explicitlypermitted that Downstream Ports be assigned to Function Numbers that arenot contiguous within the indicated range of Device Numbers, and systemsoftware is required to scan for Downstream Port Bridges at everyFunction Number within the indicated quantity of Device Numbersassociated with the Secondary Side of the Upstream Port. This field isReserved for Downstream Ports. 10:8 FPB BD Vector SizeSupported-Indicates the size of the FPB BD Vector implemented inhardware, and constrains the allowed values software is permitted towrite to the FPB BD Vector Granularity field. Defined encodings are:Value Size Allowed Granularities 000b 256 bits 8, 16, 32, 64, 128, 256001b 512 bits 8, 16, 32, 64, 128 010b  1K bits 8, 16, 32, 64 011b  2Kbits 8, 16, 32 100b  4K bits 8, 16 101b  8K bits 8 All other encodingsare Reserved If the FPB BD Vector Supported bit is Clear, then the valuein this field is undefined and must be ignored by software. 15:11Reserved 18:16 FPB MEM Low Vector Size Supported-Indicates the size ofthe Mem Low Vector implemented in hardware, and constrains the allowedvalues software is permitted to write to the FPB MEM Low Vector Startfield. Defined encodings are: Value Size Allowed Granularities 000b 256bits 1, 2, 4, 8, 16 001b 512 bits 1, 2, 4, 8 010b  1K bits 1, 2, 4 011b 2K bits 1, 2 100b  4K bits 1 All other encodings are Reserved If theFPB Mem Low Vector Supported bit is Clear, then the value in this fieldis undefined and must be ignored by software. 23:19 Reserved 26:24 FPBMEM High Vector Size Supported-Indicates the size of the Mem Low Vectorimplemented in hardware. Defined encodings are: 000b 256 bits 001b 512bits 010b  1K bits 011b  2K bits 100b  4K bits 101b  8K bits All otherencodings are Reserved If the FPB Mem High Vector Supported bit isClear, then the value in this field is undefined and must be ignored bysoftware. 31:27 Reserved

Table 3 illustrates one example implementation of an FPB BD VectorControl 1 Register. In one example, the FPB BD Vector Control 1 Registercan have an offset of 08h.

TABLE 3 FPB BD Vector Control 1 Register Bit Location RegisterDescription 0 FPB BD Vector Enable-When Set, enables the FPB BD Vectormechanism If the FPB BD Vector Supported bit is Clear, then it ispermitted for hardware to implement this bit as read only (RO), and inthis case the value in this field is undefined. Default value of thisbit is 0b. 3:1 Reserved 6:4 FPB BD Vector Granularity-The value writtenby software to this field controls the granularity of the FPB BD Vectorand the required alignment of the FPB BD Vector Start field (below).Defined encodings are: Value Granularity Start Alignment 000b  8 BDF <noconstraint> 001b  16 BDF . . . 0b 010b  32 BDF . . . 00b 011b  64 BDF .. . 000b 100b 128 BDF . . . 0000b 101b 256 BDF . . . 00000b All otherencodings are Reserved Based on the implemented FPB BD Vector size,hardware is permitted to implement as RW only those bits of this fieldthat can be programmed to non-zero values, in which case the upper orderbits are permitted but not required to be hardwired to 0. If the FPB BDVector Supported bit is Clear, then it is permitted for hardware toimplement this field as RO, and the value in this field is undefined.Default value for this field is 0000b. 18:7 Reserved 31:19 FPB BD VectorStart-The value written by software to this field controls the offsetwithin BD space at which the FPB BD Vector is applied. The valuerepresents a Bus/Device Number (bits [15:3] of an address in BDF Space),such that bit 0 of the FPB BD Vector represents the range starting fromthe value in this register up to that value plus the granularity minus 1and bit 1 represents range from this register value plus granularity upto that value plus granularity minus 1, etc. The Function Number offset(bits[2:0]) is fixed by hardware as 000b and cannot be modified.Software must program this field to a value that is naturally alignedaccording to the value in the FPB BD Vector Granularity Field asindicated here: FPB BD Vector Granularity Start Alignment Constraint0000b <no constraint> 0001b . . . 0b 0010b . . . 00b 0011b . . . 000b0100b . . . 0000b 0101b . . . 00000b If this requirement is violated,the hardware behavior is undefined. If the FPB BD Vector Supported bitis Clear, then it is permitted for hardware to implement this field asRO, and the value in this field is undefined. Default value for thisfield is 000h.

Table 4 illustrates one example implementation of an FPB BD VectorControl 2 Register. In one example, the FPB BD Vector Control 2 Registercan have an offset of 0Ch.

TABLE 4 FPB BD Vector Control 2 Register Bit Location RegisterDescription 2:0 Reserved 15:3 BD Secondary Start-The value written bysoftware to this field controls the offset within BDF space at whichType 1 Configuration Requests passing downstream through the bridge mustbe converted to Type 0. The value represents a Bus/Device Number (bits[15:3] of an address in BDF Space). The Function Number offset(bits[2:0]) is fixed by hardware as 000b and cannot be modified. Whenthe ARI Forwarding Enable bit in the Device Control 2 register is Set,then software must write bits 7:3 of this field to 00000b. If the FPB BDVector Supported bit is Clear, then it is permitted for hardware toimplement this field as RO, and the value in this field is undefined.Default value for this field is 000h. 31:16 Reserved

Table 5 illustrates one example implementation of an FPB BD VectorAccess Control Register. In one example, the FPB BD Vector AccessControl Register can have an offset of 10h.

TABLE 5 FPB BD Vector Access Control Register Bit Location RegisterDescription 7:0 FPB BD Vector Access Offset-The value in this fieldindicates the offset of the 32b portion of the FPB BD Vector that can beread or written by means of the FPB BD Vector Access Data Register. Thebits of this field map to the offset according to the value in the FPBBD Vector Size Supported field as shown here: Offset Bits This Field000b 2:0 2:0 (7:3 unused) 001b 3:0 3:0 (7:4 unused) 010b 4:0 4:0 (7:5unused) 011b 5:0 5:0 (7:6 unused) 100b 6:0 6:0 (7 unused) 101b 7:0 7:0All other encodings are Reserved Bits in this field that are unused perthe table above must be written by software as 0b, and are permitted bynot required to be implemented as RO. If the FPB BD Vector Supported bitis Clear, then it is permitted for hardware to implement this field asRO, and the value in this field is undefined. Default value for thisfield is 00h 31:8 Reserved

Table 6 illustrates one example implementation of an FPB BD VectorAccess Data Register. In one example, the FPB BD Vector Access DataRegister can have an offset of 14h.

TABLE 6 FPB BD Vector Access Data Register Bit Location RegisterDescription 31:0 FPB BD Vector Data-Reads from this register return theDW of data from the FPB BD Vector at the location determined by thevalue in the FPB BD Vector Access Offset Register. Writes to thisregister replace the DW of data from the FPB BD Vector at the locationdetermined by the value in the FPB BD Vector Access Offset Register. Ifthe FPB BD Vector Supported bit is Clear, then it is permitted forhardware to implement this field as RO, and the value in this field isundefined. Default value for this field is 0000h

Table 7 illustrates one example implementation of an FPB MEM Low VectorControl Register. In one example, the FPB MEM Low Vector ControlRegister can have an offset of 18h.

TABLE 7 FPB MEM Low Vector Control Register Bit Location RegisterDescription 0 FPB MEM Low Vector Enable-When Set, enables the FPB MEMLow Vector mechanism. If the FPB MEM Low Vector Supported bit is Clear,then it is permitted for hardware to implement this field as RO, and inthis case the value in this field is undefined. Default value of thisbit is 0b. 3:1 Reserved 7:4 FPB MEM Low Vector Granularity-The valuewritten by software to this field controls the granularity of the FPBMEM Low Vector, and the required alignment of the FPB MEM Low VectorStart field (below). Defined encodings are: Value Constraint GranularityStart Alignment 000b  1 MB <no constraint> 001b  2 MB . . . 0b 010b  4MB . . . 00b 011b  8 MB . . . 000b 100b 16 MB . . . 0000b All otherencodings are Reserved Based on the implemented FPB MEM Low Vector size,hardware is permitted to implement as RW only those bits of this fieldthat can be programmed to non-zero values, in which case the upper orderbits are permitted but not required to be hardwired to 0. If the FPB MEMLow Vector Supported bit is Clear, then it is permitted for hardware toimplement this field as RO, and the value in this field is undefined.Default value for this field is 0000b. 19:8 Reserved 31:20 FPB MEM LowVector Start-The value written by software to this field sets the baseaddress at which the FPB MEM Low Vector is applied. Software mustprogram this field to a value that is naturally aligned according to thevalue in the FPB MEM Low Vector Granularity Field as indicated in thedescription for that field (above). If this requirement is violated, thehardware behavior is undefined. If the FPB MEM Low Vector Supported bitis Clear, then it is permitted for hardware to implement this field asRO, and the value in this field is undefined. Default value for thisfield is 0000h.

Table 8 illustrates one example implementation of an FPB MEM Low VectorAccess Control Register. In one example, the FPB MEM Low Vector AccessControl Register can have an offset of 1Ch.

TABLE 8 FPB MEM Low Vector Access Control Register Bit Location RegisterDescription 6:0 FPB MEM Low Vector Access Offset-The value in this fieldindicates the offset of the 32b portion of the FPB MEM Low Vector thatcan be read or written by means of the FPB MEM Low Vector Access DataRegister. The bits of this field map to the offset according to thevalue in the FPB MEM Low Vector Granularity field as shown here: OffsetBits This Field 000b 2:0 2:0 (6:3 unused) 001b 3:0 3:0 (6:4 unused) 010b4:0 4:0 (6:5 unused) 011b 5:0 5:0 (6 unused) 100b 6:0 6:0 Bits in thisfield that are unused per the table above must be written by software as0b, and are permitted by not required to be implemented as RO. If theFPB MEM Low Vector Supported bit is Clear, then it is permitted forhardware to implement this field as RO, and the value in this field isundefined. Default value for this field is 00h 31:7 Reserved

Table 9 illustrates one example implementation of an FPB MEM Low VectorAccess Data Register. In one example, the FPB MEM Low Vector Access DataRegister can have an offset of 20h.

TABLE 9 FPB MEM Low Vector Access Data Register Bit Location RegisterDescription 31:0 FPB MEM Low Vector Data-Reads from this register returnthe DW of data from the FPB MEM Low Vector at the location determintedby the value in the FPB MEM Low Vector Access Offset Register. Writes tothis register replace the DW of data from the FPB MEM Low Vector at thelocation determinted by the value in the FPB MEM Low Vector AccessOffset Register. If the FPB MEM Low Vector Supported bit is Clear, thenit is permitted for hardware to implement this field as RO, and thevalue in this field is undefined. Default value for this field is 0000h

Table 10 illustrates one example implementation of an FPB MEM HighVector Control 1 Register. In one example, the FPB MEM High VectorControl 1 Register can have an offset of 24h.

TABLE 10 FPB MEM High Vector Control 1 Register Bit Location RegisterDescription 0 FPB MEM High Vector Enable-When Set, enables the FPB MEMHigh Vector mechanism. If the FPB MEM High Vector Supported bit isClear, then it is permitted for hardware to implement this field as RO,and in this case the value in this field is undefined. Default value ofthis bit is 0b. 3:1 Reserved 7:4 FPB MEM High Vector Granularity-Thevalue written by software to this field controls the granularity of theFPB MEM High Vector, and the required alignment of the FPB MEM HighVector Start Lower field (below). Software is permitted to select anyallowed Granularity from the table below regardless of the value in theFPB MEM High Vector Size Supported field. Defined encodings are: ValueConstraint Granularity Start Alignment 000b 256 MB <no constraint> 001b512 MB . . . 0b 010b  1 GB . . . 00b 011b  2 GB . . . 000b 100b  4 GB .. . 0000b 101b  8 GB . . . 00000b 110b  16 GB . . . 000000b 111b  32 GB. . . 0000000b Based on the implemented FPB MEM High Vector size,hardware is permitted to implement as RW only those bits of this fieldthat can be programmed to non-zero values, in which case the upper orderbits are permitted but not required to be hardwired to 0. If the FPB MEMHigh Vector Supported bit is Clear, then it is permitted for hardware toimplement this field as RO, and the value in this field is undefined.Default value for this field is 0000b. 27:8 Reserved 31:28 FPB MEM HighVector Start Lower-The value written by software to this field sets thelower bits of the base address at which the FPB MEM High Vector isapplied. Software must program this field to a value that is naturallyaligned (i.e., the lower order bits are 0′s) according to the value inthe FPB MEM High Vector Granularity Field as indicated here: FPB MEMHigh Vector Granularity Constraint 0000b <no constraint> 0001b . . . 0b0010b . . . 00b 0011b . . . 000b 0100b . . . 0000b 0101b . . . 00000b0110b . . . 000000b 0111b . . . 0000000b If this requirement isviolated, the hardware behavior is undefined. If the FPB MEM High VectorSupported bit is Clear, then it is permitted for hardware to implementthis field as RO, and the value in this field is undefined. Defaultvalue for this field is 00h.

Table 11 illustrates one example implementation of an FPB MEM HighVector Control 2 Register. In one example, the FPB MEM High VectorControl 2 Register can have an offset of 28h.

TABLE 11 FPB MEM High Vector Control 2 Register Bit Location RegisterDescription 31:0 FPB MEM High Vector Start Upper-The value written bysoftware to this field indicates bits 63:32 of the base address at whichthe FPB MEM High Vector is applied. If the FPB MEM High Vector Supportedbit is Clear, then it is permitted for hardware to implement this fieldas RO, and the value in this field is undefined. Default value for thisfield is 00000000h.

Table 12 illustrates one example implementation of an FPB MEM HighVector Access Control Register. In one example, the FPB MEM High VectorAccess Control Register can have an offset of 2Ch.

TABLE 12 FPB MEM High Vector Access Control Register Bit LocationRegister Description 7:0 FPB MEM High Vector Access Offset-The value inthis field indicates the offset of the 32b portion of the FPB BD, MEMLow or MEM High Vector that can be read or written by means of the FPBMEM High Vector Access Data Register. The bits of this field map to theoffset according to the value in the FPB MEM High Vector Granularityfield as shown here: Offset Bits This Field 000b 2:0 2:0 (7:3 unused)001b 3:0 3:0 (7:4 unused) 010b 4:0 4:0 (7:5 unused) 011b 5:0 5:0 (7:6unused) 100b 6:0 6:0 (7 unused) 101b 7:0 7:0 Bits in this field that areunused per the table above must be written by software as 0b, and arepermitted by not required to be implemented as RO. If the FPB MEM HighVector Supported bit is Clear, then it is permitted for hardware toimplement this field as RO, and the value in this field is undefined.Default value for this field is 00h 13:8 Reserved 15:14 FPB VectorSelect-The value written to this field selects the Vector to be accessedat the indicated FPB Vector Access Offset, encoded as: 00: BD 01: MEMLow 10: MEM High 11: Reserved Default value for this field may be 00b31:16 Reserved

Table 13 illustrates one example implementation of an FPB MEM HighVector Access Data Register. In one example, the FPB MEM High VectorAccess Data Register can have an offset of 30h.

TABLE 13 FPB MEM High Vector Access Data Register Bit Location RegisterDescription 31:0 FPB MEM High Vector Data-Reads from this registerreturn the DW of data from the FPB MEM High Vector at the locationdetermined by the value in the FPB MEM High Vector Access OffsetRegister. Writes to this register replace the DW of data from the FPBMEM High Vector at the location determined by the value in the FPB MEMHigh Vector Access Offset Register. If the FPB MEM High Vector Supportedbit is Clear, then it is permitted for hardware to implement this fieldas RO, and the value in this field is undefined. Default value for thisfield is 0000h

In an alternate implementation, rather than providing separate VectorAccess Offset and Vector Data registers for each vector, a single VectorAccess Offset register can be used with the addition of a field toindicate which vector is to be accessed, and a single Vector Dataregister can be used to perform the read or write operations to theindicated vector. In such an implementation, the indicator field can beimplemented as a two bit field encoded such that a value of 00 (binary)can indicate an access to the BD Vector, a value of 01 (binary) canindicate an access to the MEM Low Vector, a value of 10 (binary) canindicate an access to the MEM High Vector, and a value of 11 (binary)can indicate a reserved value.

Note that the apparatus', methods', and systems described above may beimplemented in any electronic device or system as aforementioned. Asspecific illustrations, the figures below provide exemplary systems forutilizing the invention as described herein. As the systems below aredescribed in more detail, a number of different interconnects aredisclosed, described, and revisited from the discussion above. And as isreadily apparent, the advances described above may be applied to any ofthose interconnects, fabrics, or architectures.

Referring to FIG. 11, an embodiment of a block diagram for a computingsystem including a multicore processor is depicted. Processor 1100includes any processor or processing device, such as a microprocessor,an embedded processor, a digital signal processor (DSP), a networkprocessor, a handheld processor, an application processor, aco-processor, a system on a chip (SOC), or other device to execute code.Processor 1100, in one embodiment, includes at least two cores—core 1101and 1102, which may include asymmetric cores or symmetric cores (theillustrated embodiment). However, processor 1100 may include any numberof processing elements that may be symmetric or asymmetric.

In one embodiment, a processing element refers to hardware or logic tosupport a software thread. Examples of hardware processing elementsinclude: a thread unit, a thread slot, a thread, a process unit, acontext, a context unit, a logical processor, a hardware thread, a core,and/or any other element, which is capable of holding a state for aprocessor, such as an execution state or architectural state. In otherwords, a processing element, in one embodiment, refers to any hardwarecapable of being independently associated with code, such as a softwarethread, operating system, application, or other code. A physicalprocessor (or processor socket) typically refers to an integratedcircuit, which potentially includes any number of other processingelements, such as cores or hardware threads.

A core often refers to logic located on an integrated circuit capable ofmaintaining an independent architectural state, wherein eachindependently maintained architectural state is associated with at leastsome dedicated execution resources. In contrast to cores, a hardwarethread typically refers to any logic located on an integrated circuitcapable of maintaining an independent architectural state, wherein theindependently maintained architectural states share access to executionresources. As can be seen, when certain resources are shared and othersare dedicated to an architectural state, the line between thenomenclature of a hardware thread and core overlaps. Yet often, a coreand a hardware thread are viewed by an operating system as individuallogical processors, where the operating system is able to individuallyschedule operations on each logical processor.

Physical processor 1100, as illustrated in FIG. 11, includes twocores—core 1101 and 1102. Here, core 1101 and 1102 are consideredsymmetric cores, i.e. cores with the same configurations, functionalunits, and/or logic. In another embodiment, core 1101 includes anout-of-order processor core, while core 1102 includes an in-orderprocessor core. However, cores 1101 and 1102 may be individuallyselected from any type of core, such as a native core, a softwaremanaged core, a core adapted to execute a native Instruction SetArchitecture (ISA), a core adapted to execute a translated InstructionSet Architecture (ISA), a co-designed core, or other known core. In aheterogeneous core environment (i.e. asymmetric cores), some form oftranslation, such a binary translation, may be utilized to schedule orexecute code on one or both cores. Yet to further the discussion, thefunctional units illustrated in core 1101 are described in furtherdetail below, as the units in core 1102 operate in a similar manner inthe depicted embodiment.

As depicted, core 1101 includes two hardware threads 1101 a and 1101 b,which may also be referred to as hardware thread slots 1101 a and 1101b. Therefore, software entities, such as an operating system, in oneembodiment potentially view processor 1100 as four separate processors,i.e., four logical processors or processing elements capable ofexecuting four software threads concurrently. As alluded to above, afirst thread is associated with architecture state registers 1101 a, asecond thread is associated with architecture state registers 1101 b, athird thread may be associated with architecture state registers 1102 a,and a fourth thread may be associated with architecture state registers1102 b. Here, each of the architecture state registers (1001 a, 1101 b,1102 a, and 1102 b) may be referred to as processing elements, threadslots, or thread units, as described above. As illustrated, architecturestate registers 1101 a are replicated in architecture state registers1101 b, so individual architecture states/contexts are capable of beingstored for logical processor 1101 a and logical processor 1101 b. Incore 1101, other smaller resources, such as instruction pointers andrenaming logic in allocator and renamer block 1130 may also bereplicated for threads 1101 a and 1101 b. Some resources, such asre-order buffers in reorder/retirement unit 1135, ILTB 1120, load/storebuffers, and queues may be shared through partitioning. Other resources,such as general purpose internal registers, page-table base register(s),low-level data-cache and data-TLB 1115, execution unit(s) 1140, andportions of out-of-order unit 1135 are potentially fully shared.

Processor 1100 often includes other resources, which may be fullyshared, shared through partitioning, or dedicated by/to processingelements. In FIG. 11, an embodiment of a purely exemplary processor withillustrative logical units/resources of a processor is illustrated. Notethat a processor may include, or omit, any of these functional units, aswell as include any other known functional units, logic, or firmware notdepicted. As illustrated, core 1101 includes a simplified,representative out-of-order (OOO) processor core. But an in-orderprocessor may be utilized in different embodiments. The OOO coreincludes a branch target buffer 1120 to predict branches to beexecuted/taken and an instruction-translation buffer (I-TLB) 1120 tostore address translation entries for instructions.

Core 1101 further includes decode module 1125 coupled to fetch unit 1120to decode fetched elements. Fetch logic, in one embodiment, includesindividual sequencers associated with thread slots 1101 a, 1101 b,respectively. Usually core 1101 is associated with a first ISA, whichdefines/specifies instructions executable on processor 1100. Oftenmachine code instructions that are part of the first ISA include aportion of the instruction (referred to as an opcode), whichreferences/specifies an instruction or operation to be performed. Decodelogic 1125 includes circuitry that recognizes these instructions fromtheir opcodes and passes the decoded instructions on in the pipeline forprocessing as defined by the first ISA. For example, as discussed inmore detail below decoders 1125, in one embodiment, include logicdesigned or adapted to recognize specific instructions, such astransactional instruction. As a result of the recognition by decoders1125, the architecture or core 1101 takes specific, predefined actionsto perform tasks associated with the appropriate instruction. It isimportant to note that any of the tasks, blocks, operations, and methodsdescribed herein may be performed in response to a single or multipleinstructions; some of which may be new or old instructions. Notedecoders 1126, in one embodiment, recognize the same ISA (or a subsetthereof). Alternatively, in a heterogeneous core environment, decoders1126 recognize a second ISA (either a subset of the first ISA or adistinct ISA).

In one example, allocator and renamer block 1130 includes an allocatorto reserve resources, such as register files to store instructionprocessing results. However, threads 1101 a and 1101 b are potentiallycapable of out-of-order execution, where allocator and renamer block1130 also reserves other resources, such as reorder buffers to trackinstruction results. Unit 1130 may also include a register renamer torename program/instruction reference registers to other registersinternal to processor 1100. Reorder/retirement unit 1135 includescomponents, such as the reorder buffers mentioned above, load buffers,and store buffers, to support out-of-order execution and later in-orderretirement of instructions executed out-of-order.

Scheduler and execution unit(s) block 1140, in one embodiment, includesa scheduler unit to schedule instructions/operation on execution units.For example, a floating point instruction is scheduled on a port of anexecution unit that has an available floating point execution unit.Register files associated with the execution units are also included tostore information instruction processing results. Exemplary executionunits include a floating point execution unit, an integer executionunit, a jump execution unit, a load execution unit, a store executionunit, and other known execution units.

Lower level data cache and data translation buffer (D-TLB) 1150 arecoupled to execution unit(s) 1140. The data cache is to store recentlyused/operated on elements, such as data operands, which are potentiallyheld in memory coherency states. The D-TLB is to store recentvirtual/linear to physical address translations. As a specific example,a processor may include a page table structure to break physical memoryinto a plurality of virtual pages.

Here, cores 1101 and 1102 share access to higher-level or further-outcache, such as a second level cache associated with on-chip interface1110. Note that higher-level or further-out refers to cache levelsincreasing or getting further way from the execution unit(s). In oneembodiment, higher-level cache is a last-level data cache—last cache inthe memory hierarchy on processor 1100—such as a second or third leveldata cache. However, higher level cache is not so limited, as it may beassociated with or include an instruction cache. A trace cache—a type ofinstruction cache—instead may be coupled after decoder 1125 to storerecently decoded traces. Here, an instruction potentially refers to amacro-instruction (i.e. a general instruction recognized by thedecoders), which may decode into a number of micro-instructions(micro-operations).

In the depicted configuration, processor 1100 also includes on-chipinterface module 1110. Historically, a memory controller, which isdescribed in more detail below, has been included in a computing systemexternal to processor 1100. In this scenario, on-chip interface 1110 isto communicate with devices external to processor 1100, such as systemmemory 1175, a chipset (often including a memory controller hub toconnect to memory 1175 and an I/O controller hub to connect peripheraldevices), a memory controller hub, a northbridge, or other integratedcircuit. And in this scenario, bus 1105 may include any knowninterconnect, such as multi-drop bus, a point-to-point interconnect, aserial interconnect, a parallel bus, a coherent (e.g. cache coherent)bus, a layered protocol architecture, a differential bus, and a GTL bus.

Memory 1175 may be dedicated to processor 1100 or shared with otherdevices in a system. Common examples of types of memory 1175 includeDRAM, SRAM, non-volatile memory (NV memory), and other known storagedevices. Note that device 1180 may include a graphic accelerator,processor or card coupled to a memory controller hub, data storagecoupled to an I/O controller hub, a wireless transceiver, a flashdevice, an audio controller, a network controller, or other knowndevice.

Recently however, as more logic and devices are being integrated on asingle die, such as SOC, each of these devices may be incorporated onprocessor 1100. For example in one embodiment, a memory controller hubis on the same package and/or die with processor 1100. Here, a portionof the core (an on-core portion) 1110 includes one or more controller(s)for interfacing with other devices such as memory 1175 or a graphicsdevice 1180. The configuration including an interconnect and controllersfor interfacing with such devices is often referred to as an on-core (orun-core configuration). As an example, on-chip interface 1110 includes aring interconnect for on-chip communication and a high-speed serialpoint-to-point link 1105 for off-chip communication. Yet, in the SOCenvironment, even more devices, such as the network interface,co-processors, memory 1175, graphics processor 1180, and any other knowncomputer devices/interface may be integrated on a single die orintegrated circuit to provide small form factor with high functionalityand low power consumption.

In one embodiment, processor 1100 is capable of executing a compiler,optimization, and/or translator code 1177 to compile, translate, and/oroptimize application code 1176 to support the apparatus and methodsdescribed herein or to interface therewith. A compiler often includes aprogram or set of programs to translate source text/code into targettext/code. Usually, compilation of program/application code with acompiler is done in multiple phases and passes to transform hi-levelprogramming language code into low-level machine or assembly languagecode. Yet, single pass compilers may still be utilized for simplecompilation. A compiler may utilize any known compilation techniques andperform any known compiler operations, such as lexical analysis,preprocessing, parsing, semantic analysis, code generation, codetransformation, and code optimization.

Larger compilers often include multiple phases, but most often thesephases are included within two general phases: (1) a front-end, i.e.generally where syntactic processing, semantic processing, and sometransformation/optimization may take place, and (2) a back-end, i.e.generally where analysis, transformations, optimizations, and codegeneration takes place. Some compilers refer to a middle, whichillustrates the blurring of delineation between a front-end and back endof a compiler. As a result, reference to insertion, association,generation, or other operation of a compiler may take place in any ofthe aforementioned phases or passes, as well as any other known phasesor passes of a compiler. As an illustrative example, a compilerpotentially inserts operations, calls, functions, etc. in one or morephases of compilation, such as insertion of calls/operations in afront-end phase of compilation and then transformation of thecalls/operations into lower-level code during a transformation phase.Note that during dynamic compilation, compiler code or dynamicoptimization code may insert such operations/calls, as well as optimizethe code for execution during runtime. As a specific illustrativeexample, binary code (already compiled code) may be dynamicallyoptimized during runtime. Here, the program code may include the dynamicoptimization code, the binary code, or a combination thereof.

Similar to a compiler, a translator, such as a binary translator,translates code either statically or dynamically to optimize and/ortranslate code. Therefore, reference to execution of code, applicationcode, program code, or other software environment may refer to: (1)execution of a compiler program(s), optimization code optimizer, ortranslator either dynamically or statically, to compile program code, tomaintain software structures, to perform other operations, to optimizecode, or to translate code; (2) execution of main program code includingoperations/calls, such as application code that has beenoptimized/compiled; (3) execution of other program code, such aslibraries, associated with the main program code to maintain softwarestructures, to perform other software related operations, or to optimizecode; or (4) a combination thereof.

Referring now to FIG. 12, shown is a block diagram of a second system1200 in accordance with an embodiment of the present invention. As shownin FIG. 12, multiprocessor system 1200 is a point-to-point interconnectsystem, and includes a first processor 1270 and a second processor 1280coupled via a point-to-point interconnect 1250. Each of processors 1270and 1280 may be some version of a processor. In one embodiment, 1252 and1254 are part of a serial, point-to-point coherent interconnect fabric,such as Intel's Quick Path Interconnect (QPI) architecture. As a result,the invention may be implemented within the QPI architecture.

While shown with only two processors 1270, 1280, it is to be understoodthat the scope of the present invention is not so limited. In otherembodiments, one or more additional processors may be present in a givenprocessor.

Processors 1270 and 1280 are shown including integrated memorycontroller units 1272 and 1282, respectively. Processor 1270 alsoincludes as part of its bus controller units point-to-point (P-P)interfaces 1276 and 1278; similarly, second processor 1280 includes P-Pinterfaces 1286 and 1288. Processors 1270, 1280 may exchange informationvia a point-to-point (P-P) interface 1250 using P-P interface circuits1278, 1288. As shown in FIG. 12, IMCs 1272 and 1282 couple theprocessors to respective memories, namely a memory 1232 and a memory1234, which may be portions of main memory locally attached to therespective processors.

Processors 1270, 1280 each exchange information with a chipset 1290 viaindividual P-P interfaces 1252, 1254 using point to point interfacecircuits 1276, 1294, 1286, 1298. Chipset 1290 also exchanges informationwith a high-performance graphics circuit 1238 via an interface circuit1292 along a high-performance graphics interconnect 1239.

A shared cache (not shown) may be included in either processor oroutside of both processors; yet connected with the processors via P-Pinterconnect, such that either or both processors' local cacheinformation may be stored in the shared cache if a processor is placedinto a low power mode.

Chipset 1290 may be coupled to a first bus 1216 via an interface 1296.In one embodiment, first bus 1216 may be a Peripheral ComponentInterconnect (PCI) bus, or a bus such as a PCI Express bus or anotherthird generation I/O interconnect bus, although the scope of the presentinvention is not so limited.

As shown in FIG. 12, various I/O devices 1214 are coupled to first bus1216, along with a bus bridge 1218 which couples first bus 1216 to asecond bus 1220. In one embodiment, second bus 1220 includes a low pincount (LPC) bus. Various devices are coupled to second bus 1220including, for example, a keyboard and/or mouse 1222, communicationdevices 1227 and a storage unit 1228 such as a disk drive or other massstorage device which often includes instructions/code and data 1230, inone embodiment. Further, an audio I/O 1224 is shown coupled to secondbus 1220. Note that other architectures are possible, where the includedcomponents and interconnect architectures vary. For example, instead ofthe point-to-point architecture of FIG. 12, a system may implement amulti-drop bus or other such architecture.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

Aspects of the embodiments can include one or a combination of thefollowing examples:

Example 1 is a system, method, apparatus, or storage medium withinstructions stored thereon executable to cause a machine to identify aplurality of devices in a system and assign a respective address to eachof the plurality of devices. Each device in the plurality of devices isconnected in the system by at least a respective one of a plurality ofbuses, and assigning the address to a device includes determiningwhether to assign the address according to a first addressing scheme ora second bus addressing scheme, where the first addressing schemeassigns a unique bus number within a Bus/Device/Function (BDF) addressspace to each device addressed in the first addressing scheme and thesecond bus addressing scheme assigns a unique bus-device number withinthe BDF address space.

Example 2 may include the subject matter of example 1, where aparticular Bus number is reused to address two or more devices in thesecond addressing scheme.

Example 3 may include the subject matter of any one of examples 1-2,where assigning the addresses includes designating a range of busnumbers in the BDF address space to be used to address devices accordingto the second addressing scheme.

Example 4 may include the subject matter of example 3, where the rangeof bus numbers is associated with a particular switch and the busnumbers in the range of bus numbers are used in the bus-device numbersto be assigned to each device connected to the switch.

Example 5 may include the subject matter of example 4, where the devicesconnected to the switch include a segment.

Example 6 may include the subject matter of any one of examples 1-5,where the addresses include configuration addresses.

Example 7 may include the subject matter of any one of examples 1-6,where the BDF address space includes a Peripheral Component Interconnect(PCI)-based address space.

Example 8 may include the subject matter of example 7, where eachbus-device number includes an eight bit bus number and a five bit devicenumber.

Example 9 is an apparatus including a port to receive a particularpacket, where the port includes a flattening portal bridge (FPB), theFPB includes a primary side and a secondary side, the primary sideconnects to a first set of devices addressed according to a firstaddressing scheme, and the secondary side connects to a second set ofdevices addressed according to a second addressing scheme. The FPB isfurther to determine whether to route the particular packet on theprimary side or the secondary side based on address information in theparticular packet, the first addressing scheme uses a unique bus numberwithin a Bus/Device/Function (BDF) address space for each device in thefirst set of devices, and the second bus addressing scheme uses a uniquebus-device number for each device in the second set of devices.

Example 10 may include the subject matter of example 9, where therespective bus-device numbers assigned to a plurality of devices in thesecond set of devices each include a particular bus number and adifferent device number.

Example 11 may include the subject matter of any one of examples 9-10,where the primary addressing scheme includes a legacy addressing scheme.

Example 12 may include the subject matter of any one of examples 9-11,where the BDF addressing space includes a Peripheral ComponentInterconnect Express (PCIe) configuration space.

Example 13 may include the subject matter of any one of examples 9-12,further including a plurality of ports, where the port includes aparticular one of the plurality of ports, and at least one other port inthe plurality of ports includes an FPB.

Example 14 may include the subject matter of example 13, where theplurality of ports include at least one port without an FPB.

Example 15 may include the subject matter of example 13, furtherincluding a switch, where the switch includes the plurality of ports.

Example 16 may include the subject matter of example 13, furtherincluding a root complex, where the root complex includes the pluralityof ports.

Example 17 may include the subject matter of any one of examples 9-16,further including a BD Control 1 register.

Example 18 may include the subject matter of any one of examples 9-17,further including a BD Vector Control 2 Register.

Example 19 may include the subject matter of any one of examples 9-18,further including a BD Vector Access Control Register.

Example 20 may include the subject matter of any one of examples 9-19,further including a BD Vector Access Data Register.

Example 21 may include the subject matter of any one of examples 9-20,further including a MEM Low Vector Control Register.

Example 22 may include the subject matter of any one of examples 9-21,further including a MEM Low Vector Access Control Register.

Example 23 may include the subject matter of any one of examples 9-22,further including a MEM Low Vector Access Data Register.

Example 24 may include the subject matter of any one of examples 9-23,further including a MEM High Vector Control 1 Register.

Example 25 may include the subject matter of any one of examples 9-24,further including a MEM High Vector Control 2 Register.

Example 26 may include the subject matter of any one of examples 9-25,further including a MEM High Vector Access Control Register.

Example 27 may include the subject matter of any one of examples 9-26,further including a MEM High Vector Access Data Register.

Example 28 is a storage medium having instructions stored thereon, theinstructions when executed on a machine, cause the machine to configureregisters of a device to support a primary bus address scheme in aBus/Device/Function (BDF) space and an alternate bus addressing schemethat uses the same bus number within a or memory mapped input/output(I/O) (MMIO) space in enumerating a plurality of different buses of asystem.

Example 29 may include the subject of example 28, where the instructionsare further executable to constrain a permissible range of BD to beassigned to a Secondary Side of a Root Port bridge.

Example 30 is a system including a switch device, a hierarchy of devicesconnected to the switch device, a set of one or more other devicesconnected to the switch device, where the set of one or more otherdevices is addressed according to a first addressing scheme, thehierarchy of devices is addressed according to second addressing scheme,the first addressing scheme uses a unique bus number within aBus/Device/Function (BDF) address space for each device in the first setof devices, and the second addressing scheme uses a unique bus-devicenumber for each device in the second set of devices.

Example 31 may include the subject of example 30, where the switchdevice includes a first port to connect to the hierarchy of devices, andthe first port includes bridge logic to determine whether to route aparticular packet on a primary side of the bridge utilizing the firstaddressing scheme or a secondary side of the bridge utilizing the secondaddressing scheme.

Example 32 may include the subject matter of any one of examples 30-31,further including a capability register to be encoded to selectivelyenable support for the secondary addressing scheme on a particular portof the switch.

Example 33 may include the subject matter of any one of examples, 30-32where the switch device includes a root complex

A design may go through various stages, from creation to simulation tofabrication. Data representing a design may represent the design in anumber of manners. First, as is useful in simulations, the hardware maybe represented using a hardware description language or anotherfunctional description language. Additionally, a circuit level modelwith logic and/or transistor gates may be produced at some stages of thedesign process. Furthermore, most designs, at some stage, reach a levelof data representing the physical placement of various devices in thehardware model. In the case where conventional semiconductor fabricationtechniques are used, the data representing the hardware model may be thedata specifying the presence or absence of various features on differentmask layers for masks used to produce the integrated circuit. In anyrepresentation of the design, the data may be stored in any form of amachine readable medium. A memory or a magnetic or optical storage suchas a disc may be the machine readable medium to store informationtransmitted via optical or electrical wave modulated or otherwisegenerated to transmit such information. When an electrical carrier waveindicating or carrying the code or design is transmitted, to the extentthat copying, buffering, or re-transmission of the electrical signal isperformed, a new copy is made. Thus, a communication provider or anetwork provider may store on a tangible, machine-readable medium, atleast temporarily, an article, such as information encoded into acarrier wave, embodying techniques of embodiments of the presentinvention.

A module as used herein refers to any combination of hardware, software,and/or firmware. As an example, a module includes hardware, such as amicro-controller, associated with a non-transitory medium to store codeadapted to be executed by the micro-controller. Therefore, reference toa module, in one embodiment, refers to the hardware, which isspecifically configured to recognize and/or execute the code to be heldon a non-transitory medium. Furthermore, in another embodiment, use of amodule refers to the non-transitory medium including the code, which isspecifically adapted to be executed by the microcontroller to performpredetermined operations. And as can be inferred, in yet anotherembodiment, the term module (in this example) may refer to thecombination of the microcontroller and the non-transitory medium. Oftenmodule boundaries that are illustrated as separate commonly vary andpotentially overlap. For example, a first and a second module may sharehardware, software, firmware, or a combination thereof, whilepotentially retaining some independent hardware, software, or firmware.In one embodiment, use of the term logic includes hardware, such astransistors, registers, or other hardware, such as programmable logicdevices.

Use of the phrase ‘to’ or ‘configured to,’ in one embodiment, refers toarranging, putting together, manufacturing, offering to sell, importingand/or designing an apparatus, hardware, logic, or element to perform adesignated or determined task. In this example, an apparatus or elementthereof that is not operating is still ‘configured to’ perform adesignated task if it is designed, coupled, and/or interconnected toperform said designated task. As a purely illustrative example, a logicgate may provide a 0 or a 1 during operation. But a logic gate‘configured to’ provide an enable signal to a clock does not includeevery potential logic gate that may provide a 1 or 0. Instead, the logicgate is one coupled in some manner that during operation the 1 or 0output is to enable the clock. Note once again that use of the term‘configured to’ does not require operation, but instead focus on thelatent state of an apparatus, hardware, and/or element, where in thelatent state the apparatus, hardware, and/or element is designed toperform a particular task when the apparatus, hardware, and/or elementis operating.

Furthermore, use of the phrases ‘capable of/to,’ and or ‘operable to,’in one embodiment, refers to some apparatus, logic, hardware, and/orelement designed in such a way to enable use of the apparatus, logic,hardware, and/or element in a specified manner. Note as above that useof to, capable to, or operable to, in one embodiment, refers to thelatent state of an apparatus, logic, hardware, and/or element, where theapparatus, logic, hardware, and/or element is not operating but isdesigned in such a manner to enable use of an apparatus in a specifiedmanner.

A value, as used herein, includes any known representation of a number,a state, a logical state, or a binary logical state. Often, the use oflogic levels, logic values, or logical values is also referred to as 1'sand 0's, which simply represents binary logic states. For example, a 1refers to a high logic level and 0 refers to a low logic level. In oneembodiment, a storage cell, such as a transistor or flash cell, may becapable of holding a single logical value or multiple logical values.However, other representations of values in computer systems have beenused. For example the decimal number ten may also be represented as abinary value of 1010 and a hexadecimal letter A. Therefore, a valueincludes any representation of information capable of being held in acomputer system.

Moreover, states may be represented by values or portions of values. Asan example, a first value, such as a logical one, may represent adefault or initial state, while a second value, such as a logical zero,may represent a non-default state. In addition, the terms reset and set,in one embodiment, refer to a default and an updated value or state,respectively. For example, a default value potentially includes a highlogical value, i.e. reset, while an updated value potentially includes alow logical value, i.e. set. Note that any combination of values may beutilized to represent any number of states.

The embodiments of methods, hardware, software, firmware or code setforth above may be implemented via instructions or code stored on amachine-accessible, machine readable, computer accessible, or computerreadable medium which are executable by a processing element. Anon-transitory machine-accessible/readable medium includes any mechanismthat provides (i.e., stores and/or transmits) information in a formreadable by a machine, such as a computer or electronic system. Forexample, a non-transitory machine-accessible medium includesrandom-access memory (RAM), such as static RAM (SRAM) or dynamic RAM(DRAM); ROM; magnetic or optical storage medium; flash memory devices;electrical storage devices; optical storage devices; acoustical storagedevices; other form of storage devices for holding information receivedfrom transitory (propagated) signals (e.g., carrier waves, infraredsignals, digital signals); etc, which are to be distinguished from thenon-transitory mediums that may receive information there from.

Instructions used to program logic to perform embodiments of theinvention may be stored within a memory in the system, such as DRAM,cache, flash memory, or other storage. Furthermore, the instructions canbe distributed via a network or by way of other computer readable media.Thus a machine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer), but is not limited to, floppy diskettes, optical disks,Compact Disc, Read-Only Memory (CD-ROMs), and magneto-optical disks,Read-Only Memory (ROMs), Random Access Memory (RAM), ErasableProgrammable Read-Only Memory (EPROM), Electrically ErasableProgrammable Read-Only Memory (EEPROM), magnetic or optical cards, flashmemory, or a tangible, machine-readable storage used in the transmissionof information over the Internet via electrical, optical, acoustical orother forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.). Accordingly, the computer-readablemedium includes any type of tangible machine-readable medium suitablefor storing or transmitting electronic instructions or information in aform readable by a machine (e.g., a computer)

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

In the foregoing specification, a detailed description has been givenwith reference to specific exemplary embodiments. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense. Furthermore, the foregoing use of embodiment andother exemplarily language does not necessarily refer to the sameembodiment or the same example, but may refer to different and distinctembodiments, as well as potentially the same embodiment.

What is claimed is:
 1. At least one machine accessible storage mediumhaving instructions stored thereon, the instructions when executed on amachine, cause the machine to: identify a plurality of devices in asystem, wherein each device in the plurality of devices is connected inthe system by at least a respective one of a plurality of logical buses;assign a respective address to each of the plurality of devices, whereinassigning the address to a device comprises: determining whether toassign the address according to a first addressing scheme or a secondbus addressing scheme, wherein the first addressing scheme assigns aunique bus number within a Bus/Device/Function (BDF) address space toeach device addressed in the first addressing scheme and the second busaddressing scheme assigns a unique bus-device number within the BDFaddress space.
 2. The storage medium of claim 1, wherein a particularBus number is reused to address two or more devices in the secondaddressing scheme.
 3. The storage medium of claim 1, wherein assigningthe addresses comprises designating a range of bus numbers in the BDFaddress space to be used to address devices according to the secondaddressing scheme.
 4. The storage medium of claim 3, wherein the rangeof bus numbers is associated with a particular switch and the busnumbers in the range of bus numbers are used in the bus-device numbersto be assigned to each device connected to the switch.
 5. The storagemedium of claim 4, wherein the devices connected to the switch comprisea segment.
 6. The storage medium of claim 1, wherein the addressescomprise configuration addresses.
 7. The storage medium of claim 1,wherein the BDF address space comprises a Peripheral ComponentInterconnect (PCI)-based address space.
 8. The storage medium of claim7, wherein each bus-device number comprises an eight bit bus number anda five bit device number.
 9. An apparatus comprising: a port to receivea particular packet, wherein the port comprises a flattening portalbridge (FPB), the FPB comprises a primary side and a secondary side, theprimary side connects to a first set of devices addressed according to afirst addressing scheme, and the secondary side connects to a second setof devices addressed according to a second addressing scheme; whereinthe FPB is further to determine whether to route the particular packeton the primary side or the secondary side based on address informationin the particular packet, the first addressing scheme uses a unique busnumber within a Bus/Device/Function (BDF) address space for each devicein the first set of devices, and the second bus addressing scheme uses aunique bus-device number in the BDF space for each device in the secondset of devices.
 10. The apparatus of claim 9, wherein the respectivebus-device numbers assigned to a plurality of devices in the second setof devices each comprise a particular bus number and a different devicenumber.
 11. The apparatus of claim 9, wherein the primary addressingscheme comprises a legacy addressing scheme.
 12. The apparatus of claim9, wherein the BDF addressing space comprises a Peripheral ComponentInterconnect Express (PCIe) configuration space.
 13. The apparatus ofclaim 9, further comprising a plurality of ports, wherein the portcomprises a particular one of the plurality of ports, and at least oneother port in the plurality of ports comprises an FPB.
 14. The apparatusof claim 13, wherein the plurality of ports comprise at least one portwithout an FPB.
 15. The apparatus of claim 13, further comprising aswitch, wherein the switch comprises the plurality of ports.
 16. Theapparatus of claim 13, further comprising a root complex, wherein theroot complex comprises the plurality of ports.
 17. A system comprising:a switch device; a hierarchy of devices connected to the switch device;a set of one or more other devices connected to the switch device;wherein the set of one or more other devices is addressed according to afirst addressing scheme, the hierarchy of devices is addressed accordingto second addressing scheme, the first addressing scheme uses a uniquebus number within a Bus/Device/Function (BDF) address space for eachdevice in the first set of devices, and the second addressing schemeuses a unique bus-device number in the BDF address space for each devicein the second set of devices.
 18. The system of claim 17, wherein theswitch device comprises a first port to connect to the hierarchy ofdevices, and the first port comprises bridge logic to determine whetherto route a particular packet on a primary side of the bridge utilizingthe first addressing scheme or a secondary side of the bridge utilizingthe second addressing scheme.
 19. The system of claim 17, furthercomprising a capability register to be encoded to selectively enablesupport for the secondary addressing scheme on a particular port of theswitch.
 20. The system of claim 17, wherein the switch device comprisesa root complex.